Corrosion resistant composites useful in chemical reactors

ABSTRACT

A chemical process apparatus component comprising a high purity, corrosion resistant composite including a continuous carbon fiber reinforced carbon matrix having a level of total metal impurity below about 10 ppm, preferably below about 5 ppm. Most preferably, the composite has a level of metal impurity below the detection limit of inductively coupled plasma spectroscopy for the metals Ag, Al, Ba, Be, Ca, Cd, Co, Cr, Cu, K, Mg, Mn, Mo, Na, Ni, P, Pb, Sr and Zn.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation in part of application U.S.Ser. No. 08/829,345 filed Mar. 31, 1997, now U.S. Pat. No. 5,800,924issued Sep. 1, 1998, which is a continuation of U.S. Ser. No. 08/394,605filed Feb. 27, 1995, now U.S. Pat. No. 5,683,281 issued Nov. 4, 1997.

TECHNICAL FIELD

The present invention is directed to high purity composites of carbonfiber within a carbon matrix and their preparation. More particularly,the present invention is directed to high purity composites useful ascorrosion resistant components for use in, or as part of, chemicalprocess reactors.

BACKGROUND OF THE INVENTION

The chemical process industry uses a variety of reactors for theproduction of various chemicals. In many instances the media in whichthe chemical reactions occur is highly corrosive to conventional metals.In these reactions, high temperatures are often employed in conjunctionwith aggressive chemical reagents such as acids or alkalis.

Chemical reactors usually contain various plates, baffles, stirrers,trays, tubes and the like, which are usually made from steel or othermetals. In certain chemical reactions, these parts have to be replacedon a frequent basis due to the high level of corrosion that takes place.Replacement of these parts means lengthy reactor downtime with seriouseconomic consequences.

In some chemical reactor applications, graphite has found use due to itscorrosion resistance. However, its widespread use is limited by its poorstructural properties and overall limited durability.

There is, therefore, a need to develop chemical reactor parts thatexhibit superior corrosion resistance compared to conventionally usedmaterials such as steels, and improved structural and lifetimeproperties compared to graphite. Such materials must exhibit thermal andchemical stability, corrosion resistance, and must not transferimpurities to the products of the reaction, for example, to foodadditives, catalysts, pharmaceutical compounds and the like.

High temperature composite materials, in which a ceramic or carbonmatrix is reinforced with a continuous fiber, find use in a variety ofapplications. One common application for composite materials is inaircraft brakes. In this use, the friction, or braking, material is madefrom a carbon matrix reinforced with carbon fibers (carbon/carbon orC/C). Such materials have high mechanical strength and are capable ofoperating at extreme temperatures, up to 3000° C. (in a non-oxidizingatmosphere). Composites in which both the reinforcing fiber and thematrix are ceramic find use in specialty applications such as aircraftengine parts where both strength at high temperature and low weight areneeded.

Carbon/carbon based composites offer outstanding chemical resistance.This coupled with their lightweight and structural performance makesthem ideal candidates for chemical processing equipment. An addedadvantage is that, according to the present invention, such materialscan be produced at extremely high levels of purity, thus minimizing therisks of product contamination.

It is therefore an object of the present invention to provide componentsfor use in chemical process reactors that are superior in mechanical andthermal properties to conventional graphite components.

It is a further object of the present invention to provide componentsfor use in chemical process reactors that are superior in puritycharacteristics to conventional graphite components and to conventionalcarbon/carbon materials.

It is a further object of the present invention to provide componentsfor use in chemical process reactors that are superior to conventionalmetals in corrosion resistance.

SUMMARY OF THE INVENTION

The present invention provides a corrosion resistant, high puritycarbon/carbon composite structural material consisting of carbon fiberreinforcements within a carbon matrix. This material has outstandingthermal properties, especially in non-oxidizing atmospheres. Before thepresent invention, use of carbon/carbon composite materials in thechemical process industry was not known. This was due to the inabilityto produce materials that not only exhibit good structural andmechanical properties, but that are extremely pure and will notcontaminate sensitive chemical species such as food additives,catalysts, pharmaceutical compounds and the like.

The present invention, therefore, provides a corrosion resistant, highpurity composite comprising a continuous carbon fiber reinforced carbonmatrix, having a total level of metal impurity below about 10 ppm,preferably below about 5 ppm, having an ultimate tensile strength ofgreater than about 25 ksi and a fracture toughness as measured by Izodimpact of about 5 ft-lb/in.

The present invention further provides chemical process reactorcomponents and furniture comprising the above corrosion resistant, highpurity carbon/carbon composite, the composite including a continuouscarbon fiber reinforced carbon matrix having a total level of metalimpurity below about 10 ppm, preferably below about 5 ppm, having anultimate tensile strength of greater than about 25 ksi and a fracturetoughness as measured by Izod impact of about 5 ft-lb/in. Suchcomponents can be used in processes for catalyst production of finechemicals such as catalysts, food additives, pharmaceuticals, and thelike, as well as industrial chemicals.

In one embodiment, the present invention provides a chemical processreactor floor or tray comprising the corrosion resistant, high puritycarbon/carbon composite material. In another embodiment, the presentinvention provides a reactor baffle comprising the corrosion resistant,high purity carbon/carbon material. In yet another embodiment, thepresent invention provides a tray of the type widely used indistillation columns, comprising the corrosion resistant, high puritycarbon/carbon material.

The present invention also provides a chemical process reactor apparatuscomprising at least one corrosion resistant, high purity, carbon/carboncomposite component, said composite including a continuous carbon fiberreinforced carbon matrix having a total level of metal impurity belowabout 10 ppm, preferably below about 5 ppm, and most preferably themetal impurity being below the detection limit of inductively coupledplasma spectroscopy for the metals Ag, Al, Ba, Be, Ca, Cd, Co, Cr, Cu,K, Mg, Mn, Mo, Na, Ni, P, Pb, Sr and Zn. In one embodiment, the chemicalprocess reactor vessel comprises the corrosion resistant, high puritycarbon/carbon composite.

The present invention also provides a process for the production of acorrosion resistant, high purity, carbon/carbon composite comprising:

heating a carbon fiber reinforcement to at least about 2400° C.,

impregnating the carbon fiber with a matrix precursor of high puritycarbon having less than about 10 ppm metals,

carbonizing the impregnated fabric to form a carbonized part,

densifying the carbonized part with high purity carbon having less thanabout 10 ppm metals to form a component, and

heating the component at a temperature of at least about 2400° C. toform the high purity composite.

In one embodiment, densifying the carbonized part includes purging achemical vapor deposition (CVD) processing furnace with an inert gas ata temperature of at least about 2400° C., and densifying the carbonizedpart with chemically vapor deposited carbon in the purged CVD furnace toform the component.

We have, therefore, found it possible to produce carbon/carbon materialswith the desired mechanical, thermal, chemical and physicalcharacteristics, that make these materials well suited for use in thechemical process industry, particularly for use as components inchemical reactors, including distillation columns, designed for theproduction of catalysts and other ultra pure materials and finechemicals, as well as corrosive chemicals manufactured or processed inaggressive environments.

DETAILED DESCRIPTION OF THE INVENTION

Carbon fiber reinforced carbon matrix materials, or carbon/carboncomposites, have thermal stability, high resistance to thermal shock dueto high thermal conductivity and low thermal expansion behavior (thatis, thermal expansion coefficient or TEC), chemical resistance, and havehigh toughness, strength and stiffness in high-temperature applications.

Carbon/carbon composites comprise carbon reinforcements mixed orcontacted with matrix precursors to form a "green" composite, which isthen carbonized to form the carbon/carbon composite. They may alsocomprise carbon or graphite reinforcements in which the matrix isintroduced fully or in part by chemical vapor infiltration (CVI).

The carbon reinforcements are commercially available from Amoco, DuPont,Hercules, and others, and can take the form of continuous fiber, clothor fabric, yarn, and tape (unidirectional arrays of fibers). Yarns maybe woven into desired shapes by braiding, knitting, or bymultidirectional weaving. The yarn, cloth and/or tape may be wrapped orwound around a mandrel to form a variety of shapes and reinforcementorientations. The fibers may be wrapped in the dry state or they may beimpregnated with the desired matrix precursor prior to wrapping,winding, or stacking. Such prepreg and woven structures reinforcementsare commercially available from various sources, including Fiberite,Hexcel and Cytek. The reinforcements are prepared from precursors suchas polyacrylonitrile (PAN), rayon or pitch. According to the preferredembodiment of the present invention, the reinforcement is in the form ofcontinuous fibers, more preferably in the form of a woven cloth.

Matrix precursors which may be used to form carbon/carbon compositesaccording to the present invention include liquid sources of carbon,such as phenolic resins and pitch, and gaseous sources, includinghydrocarbons such as methane, ethane, propane and the like.Representative phenolics include, but are not limited to, phenolics soldunder the trade designations USP 39 and 91LD, such as supplied byAshland Chemical, and SC1008 such as supplied by Borden Chemical.

The carbon/carbon composites useful in the present invention may befabricated by a variety of techniques. Conventionally, resin impregnatedcarbon fibers are autoclave- or press-molded into the desired shape on atool or in a die. The molded parts are heat-treated in an inertenvironment to temperatures from about 700° C. to about 2900° C. inorder to convert the organic phases to carbon. The carbonized parts arethen densified by carbon chemical vapor infiltration (CVI) or bymultiple cycle reimpregnations and carbonizations with the resinsdescribed above. Other fabrication methods include hot-pressing and thechemical vapor impregnation of dry preforms. Methods of fabrication ofcarbon/carbon composites which may be used according to the presentinvention are described in U.S. Pat. Nos. 3,174,895 and 3,462,289, whichare incorporated by reference herein.

Once the general shape of the carbon/carbon composite article isfabricated, the piece can be readily machined to precise tolerances, onthe order of about 0.1 mm or less. Further, because of the strength andmachinability of carbon/carbon composites, in addition to the shapingpossible in tne initial fabrication process, carbon/carbon compositescan be formed into shapes for components that are not possible withgraphite, for example.

The high purity carbon/carbon composite according to the presentinvention has the physical properties of conventionally producedcarbon/carbon composites, yet has improved corrosion resistance andpurity resulting from the process for the production of the corrosionresistant, high purity carbon/carbon composite of the present invention.

After the component has been formed by the densification of thecarbonized part, the component is further heat treated at 2400° C. toabout 3000° C. in a non-oxidizing or inert atmosphere to ensuregraphitization of the structure and to remove any impurities that mayhave been introduced. The period of time for this procedure iscalculated based upon graphitization time/temperature kinetics, takinginto account furnace thermal load and mass. The component may bemachined, if desired, to precise specifications and tolerances, asdiscussed above.

Component purity is established by the use of high purity matrixprecursors and carbon black fillers. For example, the phenolic resinsused should contain less than 50 ppm metals, should utilize non-metallicaccelerators for cure, and preferably should be made in a stainlesssteel reactor. Processing conditions in the manufacture of thecarbonized parts are maintained at high standards so as not to introduceany extraneous impurities.

In the chemical vapor infiltration (CVI) of the carbonized part,precautions are taken not to introduce any elemental impurities in theCVI furnace. Prior to processing the carbonized parts, the furnace ispurged by running an inert gas, such as argon, helium or nitrogen,through it for several heat treat cycles at about 2400° C. to 3000° C.

A method of producing high purity carbon/carbon composites is alsodescribed in copending U.S. Ser. No. 08/394,605, now U.S. Pat. No.5,683,281, incorporated herein by reference, and commonly assigned withthe present application.

We have found that the specific variants of carbon/carbon compositesdisclosed herein, according to the present invention, offer corrosionresistance compared to conventional metals and improved purity anddurability compared to graphites and conventional carbon/carboncomposites. A comparison of the corrosion resistance of steel ascompared to carbon/carbon composites is shown in Table 1 below.

As used herein, corrosion resistance means that the material experiencesnegligible attack, or exhibits negligible weight lose in commonly usedchemical reaction media. For example, while strong oxidizing agents,such as nitric acid, at high temperatures and high concentrations willaffect the inventive carbon/carbon composites, mild oxidizing agents andall reducing agents have no effect on the material.

                  TABLE 1                                                         ______________________________________                                                    Temperature                                                                              316                                                    Environment (deg C.)   Stainless Steel                                                                          Carbon/Carbon                               ______________________________________                                        Hydrochloric acid                                                                         25 deg C.  B          A                                           (75%)                                                                         Hydrochloric acid                                                                         Boiling point                                                                            B          A                                           (75%)                                                                         Acetic acid 25 deg C.  B          A                                           Acetic acid Boiling point                                                                            B          A                                           Sulfuric acid 25-75%                                                                      130 deg C. B          A                                           Sulfuric acid 75-                                                                         80 deg C.  B          B                                           100%                                                                          Nitric acid Boiling point                                                                            B          B                                           Ammonia aqueous                                                                           Boiling point                                                                            B          A                                           ______________________________________                                         Key A = Complete resistance to attack, B = Some attack                   

High purity carbon/carbon composites prepared according to the presentinvention were analyzed by inductively coupled plasma Spectroscopy (ICP)in comparison with conventional graphite components, also analyzed byatomic absorption spectroscopy (AAS), and with conventionalcarbon/carbon composites, analyzed by high temperature halonization. Theresults are shown in Table II below.

                  TABLE 2                                                         ______________________________________                                        Purity Levels in Graphite, Conventional C/C                                   and C/C of the Present Invention                                              Element Detection            Conventional                                                                          High Purity                              (ppm)   Limit (ICP)                                                                             Graphite   C/C     C/C                                      ______________________________________                                        Aluminum                                                                              0.1       <0.08      4       Not detected                             Calcium 0.1       0.13       10-30   Not detected                             Chromium                                                                              0.01      <0.07      <0.32   Not detected                             Copper  0.02      <0.08      <0.06   Not detected                             Iron    0.04      0.09       3-5     0.18                                     Magnesium                                                                             0.02      <0.02      3-5     Not detected                             Manganese                                                                             0.01      <0.08       0.034  Not detected                             Molybdenum                                                                            0.02      Not measured                                                                             1.0     Not detected                             Nickel  0.04      <0.01      Not detected                                                                          Not detected                             Phosphorous                                                                           0.02      Not measured                                                                             5.8     Not detected                             Potassium                                                                             4.0       <0.01      Not detected                                                                          Not detected                             Sodium  0.2       <0.05      4.8     Not detected                             Vanadium                                                                              0.02      <0.07      Not     0.24                                                                  measured                                         ______________________________________                                    

As shown in Table 2, the high purity carbon/carbon composites of thepresent invention are below the detection limit for inductively coupledplasma spectroscopy analysis for the metals Al, Ca, Cr, Cu, K, Mg, Mn,Mo, Na, Ni, and P, while these metal impurities are shown to be presentin graphite, and in conventional carbon/carbon composite materials(except in the latter, for nickel and potassium). Values reported hereinthat are lower than the ICP detection limit were obtained by glowdischarge mass spectrometry.

Carbon/carbon composites produced according to the invention were ashedand the diluted residue further analyzed by inductively coupled plasmaspectroscopy for metals content in addition to those metals testedabove. As demonstrated in Table 3 below, the concentration of thesemetals, Ag, Ba, Be, Cd, Co, Pb, Sr, and Zn, was also below the detectionlimit for the analytical technique.

                  TABLE 3                                                         ______________________________________                                        Element   Detection Limit (PPM)                                                                       High Purity C/C Level                                 ______________________________________                                        Barium    0.01          Not detected                                          Beryllium 0.01          Not detected                                          Cadmium   0.01          Not detected                                          Cobalt    0.02          Not detected                                          Lead      0.2           Not detected                                          Silver    0.02          Not detected                                          Strontium 0.02          Not detected                                          Zinc      0.02          Not detected                                          ______________________________________                                    

Carbon/carbon composites, according to the invention, can be used inchemical processing apparatus without first coating the component,although it is preferable to precoat the carbon/carbon composite priorto use, in order to lock down any particles which may have formed as aresult of the composite fabrication or machining process. Carbon/carboncomposites can readily be coated with a protective coating, such asrefractory carbides, refractory nitrides, and refractory borides.Preferred refractory coatings are silicon carbide, silicon nitride,boron carbide, boron nitride, pyrolytic boron nitride and siliconboride. Graded or layered coatings of the carbides, nitrides and boridesmay also be used. Other protective coatings which can be used to sealthe carbon/carbon composite material, such as to avoid particulation,include glasses, vitreous or glassy carbon, and pyrolitic carbon.

Additionally, polymers such as fluorocarbon polymers, which areresistant to the reaction medium employed in the apparatus may also beused to coat the carbon/carbon composite components of the presentinvention, to prevent particulation. Examples include but are notlimited to polyterafluoroethylene, polyvinylidene fluoride, polymers offluorinated ethylene-propylene, chlorotrifluoroethylene,hexafluoropropylene, and the like.

Advantages of carbon/carbon (C/C) composites over graphite, particularlywith regard to chemical processing apparatus, arise from improvedmechanical properties, namely improved strength, dimensional stability,and impact and thermal shock resistance, in part due to theincorporation of the reinforcement fibers. Representative graphitecomponents and carbon/carbon composite components prepared according tothe present invention were tested for physical, thermal and mechanicalproperties, the results for which are reported in Table 4.

                  TABLE 4                                                         ______________________________________                                        Properties of Graphite and C/C                                                Composites of the Present Invention                                                                    C/C Composite of the                                 Property        Graphite Present Invention                                    ______________________________________                                        Density (g/cc)  1.72-1.90                                                                              1.6-1.9                                              Porosity (%)     9-12     2-15                                                Hardness (Shore)                                                                              12-80    Off scale                                            Thermal Conductivity                                                                           70-130   8-500                                               (w/mK)                                                                        Thermal Exp Coeff.                                                                            2.0-3.6  1.4 (in-plane)                                       (× 10.sup.-6 in/in/deg C.                                                                        6.3 (cross-ply)                                      Emissivity      0.77     0.6-0.7                                              Ultimate Tensile Strength                                                                     0.9-1.7  25-50                                                (ksi)                                                                         Tensile Modulus (msi)                                                                         0.8-1.7  10-25                                                Flexural Strength (ksi)                                                                       1.7-13   24-44                                                Compressive strength (ksi)                                                                    4.4-22   25-30                                                Fracture Toughness (Izod)                                                                     <1.sup.  13                                                   (ft 1-lb./in)                                                                 ______________________________________                                    

Although the properties in Table 4 above were tested for compositesproduced according to a preferred embodiment of the invention, the highpurity, corrosion resistant carbon/carbon composites of the presentinvention can be produced to exhibit a density of about 1.6 to about 2g/cc, and a porosity of about 2 to about 25%. These high puritycomposites generally range in tensile strength from about 25 to about100 ksi, in tensile modulus up to about 30 msi, in flexural strength upto about 60 ksi, in compressive strength up to about 50 ksi, and infractural toughness, as measured by Izod impact, from about 5 to about25 ft-lb/in.

Such inventive high purity composites exhibit a thermal conductivity ofabout 20 to about 500 W/mK in plane and about 5 to about 200 W/mKcross-ply, thermal expansion coefficients of zero to about 2×10⁻⁶in/in/° C. in plane and about 6×10⁻⁶ in/in/° C. to about 10×10⁻⁶ in/in/°F. cross ply. Thermal emissivity of the high purity composites is about0.4 to about 0.8. The electrical resistivity of the high puritycomposites is about 1×10⁻⁴ to about 1×10⁻² ohm-cm.

According to the present invention, the high purity, corrosion resistantcarbon/carbon composites are formed into components for use in chemicalprocess reactors, such as plates, baffles, spargers, stirrers, screens,trays, tubes, pipes, lines, beds, tanks, liners, shields, reactorfloors, and the like, as well as the reactor vessel itself. As usedherein, "component" includes parts of a chemical processing apparatus,furniture or parts used within a chemical processing apparatus or itsassociated apparatus such as transport lines, distillation columns,valves, heaters, pump components, and the like, as well as all, orportions of the reactor vessel itself.

According to the invention therefore, chemical process reactorcomponents such as diffuser plates have been fabricated, comprising ahigh purity, corrosion resistant composite including a carbon fiberreinforced carbon matrix having a level of total metal impurity belowabout 10 ppm. These diffuser plates act as supports for reactantparticles within the reactor, and contain holes through which thereaction medium passes to contact the reactant particles. These andother components are preferably fabricated from composites having atotal metal impurity level below about 5 ppm, and most preferably belowthe detection limit of inductively coupled spectroscopy for the metalsAg, Al, Ba, Be, Ca, Cd, Co, Cr, Cu, K, Mg, Mn, Mo, Na, Ni, P, Pb, Sr andZn.

In another embodiment of the invention, a high purity carbon fiberfabric is partly densified with high purity CVD carbon in order torigidize the fabric and to give it structural integrity, having a fabrictensile strength on the order of about 90 to about 140 ksi. The partlydensified component is utilized as a mesh or screen to support catalystparticles in the reaction medium.

EXAMPLES OF THE INVENTION

The use of the corrosion resistant, high purity carbon/carbon of thepresent invention in chemical processing equipment or apparatus, isexemplified by the following representative applications. These examplesarc by no means intended to limit the scope of the present invention,but are presented For the purposes of providing examples of varioustypes components that can be fabricated from the inventive compositematerial, that are common to a wide variety of chemical processesreactors. Other types of reactor components and furniture known to theskilled artisan can be fabricated from the inventive composite materialdescribed within this specification.

Example 1

Catalyst Production

Precious metal catalysts such as those disclosed in U.S. Pat. No.4,600,571 are usually prepared by the deposition of a precious metalhalide, e.g. ruthenium, onto a suitable substrate, e.g. carbonparticles, followed by reduction of the metal halide to the metal. Suchcatalysts, for example, may be used in the production of ammonia.

Commercial processes used to manufacture such catalysts may includedepositing the metal halide onto the catalyst substrate from a solutionof the halide in hydrochloric acid. Such reaction usually occurs between100 and 200° C. Stainless steel components in the catalyst reactor areknown to have a limited lifetime due to severe corrosion of the steel bythe metal halide/hydrochloric acid medium. Such parts have to bereplaced on a regular basis, which results in undesirable reactordowntime.

In experimental trials, it has been found that whereas stainless steelis adversely affected by the acidic reaction medium of this process, thehigh purity, corrosion resistant carbon/carbon composite of the presentinvention is not. No weight loss has been observed in samples that havebeen immersed in the reactor during processing runs.

The use of the carbon/carbon parts according to the present inventionnot only provides reduced reactor downtime but installation of largeparts, e.g. reactor floors, is simplified due to the much reduced weightof the component made with the inventive composite as compared to thatof stainless steel. In addition, the high level of purity of theinventive carbon/carbon parts reduces the chances of contamination ofthe catalyst.

Example 2

Preparation of Industrial Acids

Common industrial organic acids are produced on a huge scale, with manybeing utilized as intermediate chemicals. Acetic acid, or aceticanhydride, for example, is used as the starting point for manyindustrial chemicals. Other acids, such as adipic acid, is used in themanufacture of man-made plastics such as nylon.

Common to many of these acid manufacturing methods is the need forcorrosion resistant reactor internals including distillation columns andpackings. Stainless steel corrodes rapidly in these environments, and asa consequence, other more exotic metals are used, such as titanium andzirconium.

Use of the inventive carbon/carbon composite components as reactorinternals and distillation column interiors provides advantages in termsof increased lifetime due to the superior corrosion resistance, reducedweight and reduced cost, especially when compared to the more expensiveexotic metals.

Example 3

Coal Gasification

In general, coal gasification turns high sulfur coal into low sulfurcoal gas, which is subsequently burned. In one variant of the processtermed "Integrated Gasification Combined Cycle", coal is turned intoelectricity. A gasifier produces fuel gases which are cleaned, and thenburned in a gas turbine to produce electricity.

The fuel gas produced is extremely corrosive and comprises ammonia,carbon monoxide, hydrochloric acid and other corrosive substances,present in the process at temperatures up to 900° C. This fuel gasattacks most known metals, making the handling of the fuel gas andsubsequent burning extremely difficult.

We have found, in experimental trial tests that carbon/carbon compositecomponents have proven extremely resistant to attack by such a fuel gas.High purity, corrosion resistant carbon/carbon composite components ofthe present invention are useful as liners or pipes for the coalgasification process.

Other examples of chemical processes in which carbon/carbon compositecomponents of the present invention are advantageously utilized arethose in which the component is to be exposed to a fluid of controlledpurity and/or a fluid which is corrosive to metal. Examples include, butare not limited to processes for the producing or utilizing organic orinorganic acids or bases (alkalis), peroxides, mild oxidation agents orreducing agents, corrosive monomers for polymerization such asvinylidene chloride, and the like.

The following advantages have been realized using the high purity,corrosion resistant composite components of the present invention inchemical processing apparatus. The improved corrosion resistance ascompared to metals, as well as the durability of the high puritycarbon/carbon composite components, results in a reduction in reactordowntime and in some instances, reactor rebuild. The durability of thehigh purity carbon/carbon composite components is due to their superiorthermal and mechanical properties. The high purity composites are alsoresistant to thermal shock and heat/cool cycles, offering an improvementover conventional graphite components. Other advantageous thermalcharacteristics are listed in Table 4, above.

An additional and unexpected benefit from the use of the high puritycarbon/carbon composite components over graphite concerned theproduction of large components. The fabrication of large graphite partsis difficult due to graphite's low mechanical properties (e.g. flexuralstrength) and graphite's inability to support its own weight. On theother hand large parts were able to be made from high puritycarbon/carbon composites with ease, for example, up to 48 inches indiameter. Further, the ease of fabrication of the high puritycarbon/carbon composite materials prior to carbonization, and theirmachinability after carbonization, permits the fabricating the furnacecomponents into any desired configuration.

Therefore, the objects of the present invention are accomplished by theproduction and use of high purity, corrosion resistant carbon/carboncomposite components for use in chemical processing. The corrosionresistance advantage of the inventive material with respect to metalssuch as steel, mechanical and purity advantages of the inventivematerial with respect to graphite, and the purity advantages of theinventive material with respect to graphite and conventionalcarbon/carbon composites has been demonstrated, as is shown above. Itshould be understood that the present invention is not limited to thespecific embodiments described above, but includes the variations,modifications and equivalent embodiments that are defined by thefollowing claims.

I claim:
 1. A chemical process apparatus component comprising a highpurity, corrosion resistant composite including a continuous carbonfiber reinforced carbon matrix having a level of total metal impuritybelow about 10 ppm, having an ultimate tensile strength of greater thanabout 25 ksi and a fracture toughness as measured by Izod impact of atleast about 5 ft-lb/in.
 2. The component of claim 1 wherein thecomposite has a level of total metal impurity below about 5 ppm.
 3. Thecomponent of claim 1 wherein the composite has a level of metal impuritybelow the detection limit of inductively coupled plasma spectroscopy forthe metals Ag, Al, Ba, Be, Ca, Cd, Co, Cr, Cu, K, Mg, Mn, Mo, Na, Ni, P,Pb, Sr and Zn.
 4. The component of claim 1 wherein the carbon fiber isselected from the group consisting of fiber, cloth, woven fabric, yarn,and tape.
 5. The component of claim 1 wherein the carbon fiber is wovenfabric.
 6. The component of claim 1 wherein the carbon matrix comprisescarbonized high purity carbon matrix precursors, wherein the precursorcontains less than about 50 ppm metals.
 7. The component of claim 6wherein the carbon matrix precursor is a gaseous hydrocarbon.
 8. Thecomponent of claim 1 wherein the carbon matrix comprises carbonized highpurity phenolic resin.
 9. The component of claim 1 wherein the carbonmatrix comprises carbonized high purity pitch.
 10. The component ofclaim 1 having an ultimate tensile strength of about 25 to about 100 ksiand a tensile modulus of about 10 to about 30 msi.
 11. The component ofclaim 1 having an ultimate tensile strength of about 25 to about 50 ksiand a tensile modulus of about 10 to about 25 msi.
 12. The component ofclaim 1 having a flexural strength of about 24 to about 60 ksi and acompressive strength of about 25 to about 50 ksi.
 13. The component ofclaim 1 having a flexural strength of about 24 to about 44 ksi and acompressive strength of about 25 to about 30 ksi.
 14. The component ofclaim 1 having a fracture toughness as measured by Izod impact of about13 to about 25 ft lb/in.
 15. The component of claim 1 having an in planethermal expansion coefficient of zero to about 2×10⁻⁶ in/in/deg C and across-ply thermal expansion coefficient of about 6 to about 10×10⁻⁶in/in/deg C.
 16. The component of claim 1 having an in-plane thermalconductivity of about 20 to about 500 W/mK and a cross-ply thermalconductivity of about 5 to about 200 W/mK.
 17. The component of claim 1having a thermal emissivity of about 0.4 to about 0.8.
 18. The componentof claim 1 having a coating selected from the group consisting ofpyrolitic carbon, glasses, resistant polymers, carbides, nitrides, andborides.
 19. The component of claim 1 having a coating selected from thegroup consisting of silicon carbide, silicon nitride, silicon boride,boron carbide, boron nitride, pyrolytic boron nitride pyrolitic carbon,vitreous carbon, and fluorocarbon polymer.
 20. The component of claim 1having an electrical resistivity of about 1×10⁻⁴ to about 1×10⁻² ohm-cm.21. The component of claim 1 selected from the group consisting ofplates, baffles, spargers, stirrers, screens, trays, tubes, pipes,lines, beds, tanks, liners, shields, reactor floors, distillationcolumns, valves, heaters, and puimp components.
 22. A chemical processapparatus comprising at least one corrosion resistant, high purity,carbon/carbon composite component, said high purity composite includinga continuous carbon fiber reinforced carbon matrix having a level oftotal metal impurity below about 10 ppm, having an ultimate tensilestrength of greater than about 25 ksi and a fracture toughness asmeasured by Izod impact of at least about 5 ft-lb/in.
 23. The apparatusof claim 22 wherein the total metal impurity level is below about 5 ppm.24. The apparatus of claim 22 wherein the metal impurity level is belowthe detection limit of inductively coupled plasma spectroscopy for themetals Ag, Al, Ba, Be, Ca, Cd, Co, Cr, Cu, K, Mg, Mn, Mo, Na, Ni, P, Pb,Sr and Zn.
 25. The apparatus of claim 22 further comprising at least aportion of a reactor vessel.
 26. The apparatus of claim 22 furthercomprising at least one component selected from the group consisting ofplates, baffles, spargers, stirrers, screens, trays, tubes, pipes,lines, beds, tanks, liners, shields, reactor floors, distillationcolumns, valves, heaters, and pump components.
 27. The apparatus ofclaim 22 wherein the component has an ultimate tensile strength of about25 to about 100 ksi and a tensile modulus of about 10 to about 30 msi.28. The apparatus of claim 22 wherein the component has, an ultimatetensile strength of about 25 to about 50 ksi and a tensile modulus ofabout 10 to about 25 msi.
 29. The apparatus of claim 22 wherein thecomponent has a flexural strength of about 24 to about 60 ksi and acompressive strength of about 25 to about 50 ksi.
 30. The apparatus ofclaim 22 wherein the component has a flexural strength of about 24 toabout 44 ksi and a compressive strength of about 25 to about 30 ksi. 31.The apparatus of claim 22 wherein the component has a fracture toughnessas measured by Izod impact of about 13 to about 25 ft lb/in.
 32. Theapparatus of claim 22 wherein the carbon fiber is selected from thegroup consisting of fiber, cloth, woven fabric, yarn, and tape.
 33. Theapparatus of claim 22 wherein the component has a coating selected fromthe group consisting of pyrolitic carbon, glasses, resistant polymers,carbides, nitrides, and borides.
 34. The apparatus of claim 22 whereinthe component has a coating selected from the group consisting ofsilicon carbide, silicon nitride, silicon boride, boron carbide, boronnitride, pyrolytic boron nitride pyrolitic carbon, vitreous carbon, andfluorocarbon polymer.
 35. A chemical process support componentcomprising a high purity, corrosion resistant continuous carbon fiberwoven fabric, partly densified with high purity CVD carbon sufficient torigidize the fabric and to provide structural integrity to the resultingcomposite material, wherein the composite material has a level of totalmetal impurity below about 10 ppm, and a fabric tensile strength greaterthan about 90 ksi.